Semiconductor structures, memory cells and devices comprising ferroelectric materials, systems including same, and related methods

ABSTRACT

A semiconductor structure includes an electrode, a ferroelectric material adjacent the electrode, the ferroelectric material comprising an oxide of at least one of hafnium and zirconium, the ferroelectric material doped with bismuth, and another electrode adjacent the ferroelectric material on an opposite side thereof from the first electrode. Related semiconductor structures, memory cells, semiconductor devices, electronic systems, and related methods are disclosed.

TECHNICAL FIELD

Embodiments disclosed herein relate to semiconductor structuresincluding one or more ferroelectric materials, to related memory cells,to methods of forming such semiconductor structures and memory cells,and to memory devices and systems including such devices. Moreparticularly, embodiments of the disclosure relate to ferroelectricsemiconductor structures and memory cells including ferroelectricmaterials including doped hafnium oxide materials, to methods of formingsuch semiconductor structures and memory cells, to memory devicesincluding such cells, and to systems including such devices.

BACKGROUND

Non-volatile memory devices are an important element of electronicsystems due to their ability to maintain data absent a power supply.Ferroelectric random-access memory (FeRAM, FRAM) cells have beenconsidered for use in non-volatile memory devices. Some non-volatilememory cells include ferroelectric materials exhibiting a switchablepolarization responsive to application of an electric field (e.g., abias voltage). Ferroelectric materials may include at least twopolarization states, which polarization states may be switched by theapplication of the electric field. The polarization state of theferroelectric material in a FeRAM cell may be used to determine a logicstate (e.g., a 1 or a 0) of the FeRAM cell. After removal of theelectric field, the polarization state of the ferroelectric material mayremain stable for at least some period of time. Accordingly, theferroelectric material may be suitable for use in a non-volatile memorydevice, eliminating the need to refresh the cell periodically.

Perovskite materials, such as lead zirconate titanate (PZT), havecommonly been used as ferroelectric materials in FeRAM cells. However,such conventional ferroelectric materials often fall short in terms ofbit density and scalability because perovskite materials exhibit lowremnant polarization (P_(r)), a strength of which may correlate to areadout signal for the associated memory cell. For FeRAM cells, thethickness of the ferroelectric PZT film must be up to about 200 nm toachieve suitable properties since PZT loses its ferroelectric propertiesat lower thicknesses. Thus, the use of conventional ferroelectricmaterials for memory devices having a feature size of 20 nm or less hasbeen limited. In addition, conventional ferroelectric materials, such asPZT, possess limited compatibility with standard semiconductorprocessing techniques.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a capacitor including aferroelectric material, according to embodiments of the disclosure;

FIG. 2 is a cross-sectional view of a memory cell including thecapacitor, according to embodiments of the disclosure;

FIG. 3 is a simplified block diagram of a system implemented accordingto one or more embodiments of the disclosure;

FIG. 4 is a schematic of a system including FeRAM cells having acapacitor, according to embodiments of the disclosure;

FIG. 5A is a graph comparing a hysteresis curve of a bismuth-dopedferroelectric material, according to embodiments of the disclosure,compared to a hysteresis curve of a conventional undoped ferroelectricmaterial;

FIG. 5B is a graph of a signal strength vs. cycle number of a memorycell including the bismuth-doped ferroelectric material, according toembodiments of the disclosure, compared to a signal strength vs. cyclenumber of a conventional memory cell including the conventionalferroelectric material; and

FIG. 5C is a graph illustrating a crystal phase of the ferroelectricmaterial including the bismuth compared to the conventionalferroelectric material.

DETAILED DESCRIPTION

The illustrations included herewith are not meant to be actual views ofany particular systems or semiconductor structures, but are merelyidealized representations that are employed to describe embodimentsherein. Elements and features common between figures may retain the samenumerical designation except that, for ease of following thedescription, for the most part, reference numerals begin with the numberof the drawing on which the elements are introduced or most fullydescribed.

The following description provides specific details, such as materialtypes, material thicknesses, and processing conditions in order toprovide a thorough description of embodiments described herein. However,a person of ordinary skill in the art will understand that theembodiments disclosed herein may be practiced without employing thesespecific details. Indeed, the embodiments may be practiced inconjunction with conventional fabrication techniques employed in thesemiconductor industry. In addition, the description provided hereindoes not form a complete description of a semiconductor structure or amemory cell comprising a ferroelectric material, or a completedescription of a process flow for manufacturing such semiconductorstructures or memory cells. The structures described below do not form acomplete semiconductor structure or a complete memory cell. Only thoseprocess acts and structures necessary to understand the embodimentsdescribed herein are described in detail below. Additional acts to forma complete semiconductor structure or memory cell including thestructures described herein may be performed by conventional techniques.

According to embodiments disclosed herein, a ferroelectric material mayinclude a metal oxide doped with bismuth. In some embodiments, the metaloxide includes hafnium oxide (HfO₂, also referred to in the art as“hafnia”), zirconium oxide (ZrO₂, also referred to in the art as“zirconia”), or a combination thereof. The metal oxide may becrystallized to form the ferroelectric material. The ferroelectricmaterial may be doped with between about 0.1 atomic percent (at. %)bismuth and about 10.0 atomic percent bismuth, based on the metal atoms(e.g., non-oxygen atoms) in the ferroelectric material. Theferroelectric material may include hafnium bismuth oxide (HfBiO_(x)),hafnium zirconium bismuth oxide (HfZrBiO_(x)), zirconium bismuth oxide(ZrBiO_(x)), hafnium zirconate (HfZrO₄), another hafnium-containingmaterial, another zirconium-containing material, other ferroelectricmaterials doped with bismuth, or combinations thereof. The bismuth maybe uniformly distributed throughout a thickness of the ferroelectricmaterial. In other embodiments, the ferroelectric material may exhibit avarying concentration of bismuth throughout a thickness thereof. In someembodiments, the ferroelectric material may include at least anotherdopant, such as at least one of magnesium, yttrium, strontium, niobium,tantalum, lanthanum, gadolinium, vanadium, phosphorus, potassium,scandium, ruthenium, selenium, calcium, barium, aluminum, arsenic, andindium. The ferroelectric material may exhibit an orthorhombic crystalphase. In some embodiments, the ferroelectric material may be formed ona substrate exhibiting a crystal phase other than orthorhombic (e.g.,tetragonal, cubic, hexagonal, rhombohedral). In other embodiments, theferroelectric material may overlie (e.g., be formed on) a materialexhibiting an amorphous phase and may exhibit a substantially uniformand orthorhombic crystal phase. The ferroelectric material may be usedin one or more of a ferroelectric semiconductor structure, aferroelectric memory cell, a ferroelectric field effect transistor(FeFET), a ferroelectric tunnel junction (FTJ), or another ferroelectricdevice.

In some embodiments, the ferroelectric material may exhibit improvedferroelectric properties compared to conventional ferroelectricmaterials. In some embodiments, the ferroelectric material may exhibitup to a twenty-five percent increase in a magnitude of a remnantpolarization and a value of 2 P, which is equal to a difference betweenthe positive remnant polarization and the negative polarization remnantof the ferroelectric material after removal of an external electricfield. The increase in the remnant polarization may correspond to anincreased readout signal during use and operation of an associatedmemory cell. Accordingly, a memory cell including the ferroelectricmaterial may exhibit an improved memory readout signal compared to amemory cell including a conventional ferroelectric material. In someembodiments, a memory cell including the ferroelectric material of thepresent disclosure may have a useful life that is longer than a usefullife of a memory cell including a conventional ferroelectric material(e.g., may be cycled more times prior to exhibiting reducedferroelectric properties).

As used herein, the term “doped” means and includes a material thatincludes an impurity that may alter or influence a crystal lattice ofthe material to modify electric properties (e.g., electric conductivity,ferroelectricity, etc.) of the material. In some instances, the dopantmay inhabit lattice sites in the crystal lattice of the material.

FIG. 1 illustrates a capacitor 100 including a ferroelectric material104. The capacitor 100 may form a part of a memory cell according toembodiments of the disclosure and may include a bottom electrode 102,the ferroelectric material 104 over the bottom electrode 102, and a topelectrode 106 over the ferroelectric material 104. The capacitor 100 maybe, for example, a metal-insulator-metal (MIM) capacitor. While thecapacitor 100 is described and illustrated as being used inferroelectric memory cells, the disclosure is not so limited and thecapacitor 100 may be used in other non-volatile memory cells.

The bottom electrode 102 may include a conductive material. In someembodiments, the bottom electrode 102 includes titanium, titaniumnitride (TiN), titanium aluminum nitride (TiAlN), tantalum nitride(TaN), tungsten, tungsten nitride (WN), ruthenium, iridium, platinum, asilicon-containing material (e.g., titanium silicon nitride (TiSiN),tungsten silicide (WSi_(x))), a metal silicide, polysilicon, anotherconductive material, or combinations thereof. The bottom electrode 102may be formed by sputtering, atomic layer deposition (ALD), chemicalvapor deposition (CVD), physical vapor deposition (PVD), plasma enhancedchemical vapor deposition (PECVD), low pressure chemical vapordeposition (LPCVD), or other suitable process.

The ferroelectric material 104 may directly overlie and contact thebottom electrode 102. The ferroelectric material 104 may include amaterial that exhibits a polarization (e.g., a displacement ofoppositely charged ions to create a dipole moment) that is switchable byan external electric field during use and operation of a memory cellincluding the ferroelectric material 104. In other words, theferroelectric material 104 may be formed of a material formulated toexhibit a switchable polarization responsive to exposure to a switchingvoltage, typically in an opposite direction as the initially appliedelectric field. In addition, the ferroelectric material 104 may beformulated to exhibit a remnant polarization (P_(r)) that may remainafter removal of the external electric field. In other words, theferroelectric material 104 may be formulated to exhibit a non-zeropolarization after an external electric field is removed (e.g., when theferroelectric material 104 is not exposed to an external electricfield). A direction of such polarization may be dependent on thedirection and the history of the electric field previously applied tothe ferroelectric material 104. Accordingly, the ferroelectric material104 may exhibit hysteresis. As a result, the polarization of theferroelectric material 104 may be interpreted as a logic state (e.g., a1 or a 0) of the associated memory cell.

The ferroelectric material 104 may include a metal oxide doped withbismuth. In some embodiments, the metal oxide may include one or more ofhafnium oxide, zirconium oxide, hafnium zirconate (HfZrO₄), anotherhafnium-containing material, another zirconium-containing material, andcombinations thereof.

In some embodiments, the ferroelectric material 104 comprises hafniumoxide doped with bismuth. In some such embodiments, the ferroelectricmaterial 104 may include a material including hafnium, bismuth, andoxygen atoms and may be referred to herein as hafnium bismuth oxide. Forconvenience, the composition of hafnium bismuth oxide may be abbreviatedas “HfBiO_(x),” which does not indicate the stoichiometry of thehafnium, bismuth, and oxygen atoms in the ferroelectric material 104. Inother embodiments, the ferroelectric material 104 may include zirconiumoxide doped with bismuth. In some such embodiments, the ferroelectricmaterial 104 may include zirconium, bismuth, and oxygen atoms and may bereferred to herein as zirconium bismuth oxide. For convenience, thecomposition of zirconium bismuth oxide may be abbreviated as “ZrBiO_(x)”which does not indicate the stoichiometry of the zirconium, bismuth, oroxygen atoms in the ferroelectric material. In yet other embodiments,the ferroelectric material 104 may include hafnium zirconium bismuthoxide, which may be abbreviated as “HfZrBiO_(x)” and which does notindicate the stoichiometry of hafnium, zirconium, bismuth, and oxygen inthe ferroelectric material 104.

The ferroelectric material 104 may include between about 0.1 atomicpercent (at. %) and about 10.0 atomic percent bismuth, based on themetal atoms of the metal oxide and the dopant (i.e., based on non-oxygenatoms of the ferroelectric material 104). Stated another way, bismuthmay constitute between about 0.1 atomic percent and about 10.0 atomicpercent of the metals and the dopant material in the ferroelectricmaterial 104 (e.g., based on the non-oxygen atoms in the ferroelectricmaterial 104). By way of nonlimiting example, bismuth may constitutebetween about 0.1 atomic percent and about 0.3 atomic percent, betweenabout 0.3 atomic percent and about 0.5 atomic percent, between about 0.5atomic percent and about 1.0 atomic percent, between about 1.0 atomicpercent and about 3.0 atomic percent, between about 3.0 atomic percentand about 5.0 atomic percent, or between about 5.0 atomic percent andabout 10.0 atomic percent of the ferroelectric material 104, excludingthe oxygen atoms in the ferroelectric material 104. In some embodiments,bismuth constitutes about 0.3 atomic percent of the ferroelectricmaterial 104, excluding the oxygen atoms.

Since, in some embodiments, the ferroelectric material 104 may compriseabout two oxygen atoms for every metal atom (for every atom of hafnium,zirconium, bismuth, or other dopant atom), bismuth may constitutebetween about 0.15 atomic percent and about 5.0 atomic percent of theferroelectric material 104, including the oxygen atoms.

In some embodiments, the ferroelectric material 104 may include an oxidehaving the general formula Hf_(x)Zr_((1-x-y))Bi_(y)O_(z), wherein x isbetween about 0 and about 1.0, y is between about 0.01 and about 0.10,and z is between about 1.0 and about 3.0. In some embodiments, an atomicpercent of hafnium may be greater than an atomic percent of zirconium.In some such embodiments, x may be between about 0.50 and about 0.99,such as between about 0.50 and about 0.60, between about 0.60 and about0.70, between about 0.70 and about 0.80, between about 0.80 and about0.90, or between about 0.90 and about 0.99, and y may be between about 0and about 0.49, such as between about 0 and about 0.10, between about0.10 and about 0.20, between about 0.20 and about 0.30, between about0.30 and about 0.40, or between about 0.40 and about 0.49. A value of ymay be between about 0.01 and about 0.10, such as between about 0.001and about 0.003, between about 0.003 and about 0.005, between about0.005 and about 0.01, between about 0.01 and about 0.03, between about0.03 and about 0.05, or between about 0.05 and about 0.10. In someembodiments, z is equal to about 2.0.

The ferroelectric material 104 may exhibit a uniform concentration ofbismuth throughout a thickness thereof (e.g., throughout a verticaldirection illustrated in FIG. 1). In some such embodiments, theferroelectric material 104 may exhibit substantially the same atomicpercent of bismuth proximate the bottom electrode 102 as an atomicpercent of bismuth proximate the top electrode 106. Similarly, theferroelectric material 104 may exhibit substantially the same atomicpercent of bismuth at a central portion thereof (e.g., at a locationlocated about a same distance from the top electrode 106 as from thebottom electrode 102) as an atomic percent of bismuth proximate each ofthe bottom electrode 102 and the top electrode 106.

In other embodiments, the ferroelectric material 104 may exhibit anon-uniform atomic percent of bismuth across a thickness thereof. Insome such embodiments, the ferroelectric material 104 may exhibit agradient of bismuth. Accordingly, different portions of theferroelectric material 104 may exhibit a different atomic percent ofbismuth than other portions thereof. By way of nonlimiting example, someportions of the ferroelectric material 104 may be free of bismuth whileother portions thereof may include differing atomic percentages ofbismuth. In some embodiments, portions of the ferroelectric material 104proximate the bottom electrode 102 and the top electrode 106 may includea greater atomic percent of bismuth than portions of the ferroelectricmaterial 104 distal from the bottom electrode 102 and the top electrode106. In other embodiments, portions of the ferroelectric material 104proximate the bottom electrode 102 and the top electrode 106 may includea lesser atomic percent of bismuth than portions of the ferroelectricmaterial 104 distal from the bottom electrode 102 and the top electrode106.

The ferroelectric material 104 may further include at least anotherdopant in addition to bismuth. The another dopant may be selected fromthe group consisting of magnesium, yttrium, strontium, niobium,tantalum, lanthanum, gadolinium, vanadium, phosphorus, potassium,scandium, ruthenium, selenium, calcium, barium, aluminum, arsenic,indium, and silicon. In some embodiments, the at least another dopantincludes magnesium. In some such embodiments, the ferroelectric material104 may include bismuth and magnesium. In embodiments where theferroelectric material 104 includes hafnium oxide, the ferroelectricmaterial 104 may comprise hafnium bismuth magnesium oxide (HfBiMgO_(x)).In other embodiments, the ferroelectric material 104 may include hafniumzirconium bismuth magnesium oxide (HfZrBiMgO_(x)). In yet otherembodiments, the ferroelectric material 104 may include zirconiumbismuth magnesium oxide (ZrBiMgO_(x)). In other embodiments, theferroelectric material 104 may include aluminum hafnium bismuth oxide(AlHfBiO_(x)), aluminum zirconium bismuth oxide (AlZrBiO_(x)), oraluminum hafnium zirconium bismuth oxide (AlHfZrBiO_(x)).

An atomic percent of the another dopant in the ferroelectric material104 may be between about 0.1 atomic percent and about 25.0 atomicpercent, based on the metal atoms of the metal oxide, the bismuth, andthe another dopant (i.e., based on non-oxygen atoms of the ferroelectricmaterial 104). In some embodiments, an atomic percent of the anotherdopant and the bismuth may be between about 0.1 atomic percent and about0.3 atomic percent, between about 0.3 atomic percent and about 0.5atomic percent, between about 0.5 atomic percent and about 1.0 atomicpercent, between about 1.0 atomic percent and about 3.0 atomic percent,between about 3.0 atomic percent and about 5.0 atomic percent, betweenabout 5.0 atomic percent and about 10.0 atomic percent, or between about10.0 atomic percent and about 25.0 atomic percent of the ferroelectricmaterial 104, excluding oxygen. In other embodiments, an atomic percentof each of bismuth and the another dopant may be between about 0.1atomic percent and about 10.0 atomic percent. In other embodiments, theatomic percent of the another dopant in the ferroelectric material 104may be between about 0.1 atomic percent and about 10.0 atomic percent,based on the metal atoms of the metal oxide, the bismuth, and theanother dopant (i.e., based on non-oxygen atoms of the ferroelectricmaterial 104). In some embodiments, such as where the ferroelectricmaterial 104 is doped with silicon, the ferroelectric material 104 maycomprise hafnium silicate (HfSiO_(x)) doped with bismuth.

The ferroelectric material 104 may exhibit a uniform concentration ofthe another dopant throughout a thickness thereof. In some suchembodiments, the ferroelectric material 104 may exhibit substantiallythe same atomic percent of the another dopant proximate the bottomelectrode 102 as an atomic percent of the another dopant proximate thetop electrode 106. Similarly, the ferroelectric material 104 may exhibitsubstantially the same atomic percent of the another dopant at a centralportion thereof (e.g., at a location located about a same distance fromthe top electrode 106 as from the bottom electrode 102).

In other embodiments, the ferroelectric material 104 may exhibit anon-uniform atomic percent of the another dopant across a thicknessthereof. In some such embodiments, the ferroelectric material 104 mayexhibit a gradient of the another dopant. Accordingly, some portions ofthe ferroelectric material 104 may exhibit a different atomic percent ofthe another dopant than other portions thereof. By way of nonlimitingexample, different portions of the ferroelectric material 104 may befree of the another dopant while other portions thereof may include arelatively greater atomic percent of the another dopant. In someembodiments, portions of the ferroelectric material 104 proximate thebottom electrode 102 and the top electrode 106 may exhibit a greateratomic percent of the another dopant than portions of the ferroelectricmaterial 104 distal from the bottom electrode 102 and the top electrode106. In other embodiments, portions of the ferroelectric material 104proximate the bottom electrode 102 and the top electrode 106 may exhibita lesser atomic percent of the another dopant than portions of theferroelectric material 104 distal from the bottom electrode and the topelectrode 106. In some embodiments, portions of the ferroelectricmaterial 104 having a lower atomic percent of bismuth may exhibit agreater atomic percent of the another dopant. Similarly, portions of theferroelectric material 104 having a greater atomic percent of bismuthmay exhibit a lower atomic percent of the another dopant.

The ferroelectric material 104 may have a thickness between about 10 Åand about 200 Å, such as between about 10 Å and about 20 Å, betweenabout 20 Å and about 30 Å, between about 30 Å and about 50 Å, betweenabout 50 Å and about 100 Å, or between about 100 Å and about 200 Å. Insome embodiments, the thickness of the ferroelectric material 104 isabout 10 Å. In other embodiments, the thickness of the ferroelectricmaterial 104 may be about 100 Å. The ferroelectric material 104 may havea lesser thickness compared to conventional ferroelectric materials andstill exhibit desired ferroelectric properties and may not exhibitcurrent leakage therethrough. It is believed that the bismuth in theferroelectric material 104 facilitates sufficient ferroelectricproperties in the ferroelectric material 104, even at the lesserthicknesses relative to conventional ferroelectric materials. Comparedto conventional ferroelectric materials, the ferroelectric material 104may exhibit a lower operation voltage. Without wishing to be bound byany particular theory, it is believed that the bismuth of theferroelectric material 104 facilitates desired ferroelectric propertiesat relatively lower thicknesses compared to conventional ferroelectricmaterials.

The ferroelectric material 104 may be formed by one or more of ALD, CVD,PVD, PECVD, LPCVD, or other suitable process. In some embodiments, theferroelectric material 104 is formed by sputtering. In some suchembodiments, different components of the ferroelectric material 104 maybe sputtered simultaneously. In some such embodiments, a depositionchamber (e.g., a sputtering chamber) may include a plurality of targets.The targets may include bismuth oxide (B₂O₃) and at least one metaloxide target. In some embodiments, the at least one metal oxide targetmay include at least one of hafnium oxide and zirconium oxide. In someembodiments, the deposition chamber may include at least a bismuth oxidetarget, at least a hafnium oxide target, and at least a zirconium oxidetarget.

In some embodiments, the bismuth oxide and the at least one metal oxidetarget may be sputtered simultaneously to form the ferroelectricmaterial 104 exhibiting a uniform atomic percent of bismuth therethroughand comprising at least one of hafnium oxide and zirconium oxide. One ormore parameters (e.g., a power density applied to each target) may beadjusted to control a composition of the ferroelectric material formedby co-sputtering. In some embodiments, a power density applied to the atleast one metal oxide target may be greater than a power density appliedto the bismuth oxide target.

In some embodiments, the deposition chamber may further include at leastone target comprising a dopant material other than bismuth. By way ofnonlimiting example, the deposition chamber may include at least onetarget comprising the at least another dopant and configured toresputter at least one of magnesium, yttrium, strontium, niobium,tantalum, lanthanum, gadolinium, vanadium, phosphorus, potassium,scandium, ruthenium, selenium, calcium, barium, aluminum, arsenic,indium, and silicon. In some embodiments, the target of the at leastanother dopant may comprise an oxide of the at least another dopant.

In other embodiments, the ferroelectric material 104 may be formed byatomic layer deposition or chemical vapor deposition. In some suchembodiments, an atomic percent of the bismuth may not be uniform acrossa thickness of the ferroelectric material 104. Similarly, an atomicpercent of one or more metal oxides may not be uniform across athickness of the ferroelectric material 104.

Atomic vapor deposition and chemical vapor deposition techniques areknown in the art and are, therefore, not described in detail herein. Byway of nonlimiting example, a first portion of the ferroelectricmaterial 104 may be formed by introducing at least one metal precursorinto a deposition chamber. An oxidizer (e.g., oxygen, ozone, water,hydrogen peroxide, etc.) may be introduced into the deposition chamberto oxidize the at least one metal oxide precursor and form a metal on anexposed surface of a substrate or an electrode (e.g., the bottomelectrode 102). One or more cycles may be performed to form a desiredthickness of the at least one metal oxide. In some embodiments, one ormore cycles of bismuth oxide deposition may be performed, such as bycycling a bismuth precursor followed by an oxygen source to form bismuthoxide on the surface of the material. Accordingly, in some embodiments,the ferroelectric material 104 may include a first portion (e.g., afirst layer) comprising or consisting essentially of the at least onemetal oxide, a second portion (e.g., a second layer) comprising orconsisting essentially of bismuth oxide over the first portion, and athird portion (e.g., a third layer) comprising or consisting essentiallyof the at least one metal oxide over the bismuth oxide. Theferroelectric material 104 may include a plurality of distinct portionsof the bismuth oxide and a plurality of portions of the at least onemetal oxide. In some embodiments, the ferroelectric material 104 mayinclude one or more distinct portions of another dopant, as describedabove.

The ferroelectric material 104 may exhibit a crystal phase such that theferroelectric material 104 exhibits ferroelectric properties. In someembodiments, a crystal phase of the ferroelectric material 104 may beorthorhombic. The ferroelectric material 104 may exhibit a spontaneouselectric polarization that may be reversed responsive to exposure to anexternal electric field and may exhibit a nonzero remnant polarization(P_(r)) after removal of the external electric field. In other words,the ferroelectric material 104 may exhibit a hysteresis. Surprisingly,forming the ferroelectric material 104 with bismuth improvesferroelectric properties of the ferroelectric material 104, even thoughbismuth is not a rare earth element, as are many other materials thatmay induce ferroelectric properties in metal oxide materials. Withoutwishing to be bound by any particular theory, it is believed that thecomposition of the ferroelectric material 104, and the method offormation thereof, facilitates formation of an orthorhombic crystalphase and ferroelectric properties.

After forming the ferroelectric material 104, the ferroelectric materialmay be annealed to induce a desired crystal phase in the ferroelectricmaterial 104. In some embodiments, the ferroelectric material 104 may beannealed to form an orthorhombic crystal phase. In some embodiments, theferroelectric material 104 is exposed to a temperature between about400° C. and about 800° C., such as between about 400° C. and about 600°C., or between about 600° C. and about 800° C. for a time between about10 seconds and about 1 hour, such as between about 10 seconds and about30 seconds, between about 30 seconds and about 1 minute, between about 1minute and about 10 minutes, between about 10 minutes and about 30minutes, or between about 30 minutes and about 1 hour. In someembodiments, the ferroelectric material 104 is exposed to a temperatureof about 600° C. for about 30 seconds. However, the disclosure is not solimited and the ferroelectric material 104 may be annealed at adifferent temperature or for a different length of time. In otherembodiments, the ferroelectric material 104 may exhibit a desiredcrystalline phase (e.g., the orthorhombic phase) during formationthereof. By way of nonlimiting example, the ferroelectric material 104may be formed in an orthorhombic phase when the ferroelectric material104 is formed by ALD or CVD.

The top electrode 106 may directly overlie and contact the ferroelectricmaterial 104. The top electrode 106 may include a conductive material.In some embodiments, the top electrode 106 includes titanium, titaniumnitride, titanium aluminum nitride, tantalum nitride, tungsten, tungstennitride, ruthenium, iridium, platinum, a silicon-containing material(e.g., titanium silicon nitride, tungsten silicide), a metal silicide,polysilicon, another conductive material, or combinations thereof. Thetop electrode 106 may be formed by sputtering, atomic layer deposition,chemical vapor deposition, physical vapor deposition, plasma enhancedchemical vapor deposition, low pressure chemical vapor deposition, orother suitable process.

In some embodiments, the top electrode 106 may comprise the samematerial as the bottom electrode 102. In other embodiments, the topelectrode 106 includes a material that is different than the bottomelectrode 102.

Accordingly, in one embodiment, a semiconductor structure comprises anelectrode, another electrode, and a ferroelectric material comprising anoxide of at least one of hafnium, zirconium, and bismuth between theelectrode and the another electrode.

Accordingly, in one embodiment, a method of forming a semiconductorstructure comprises forming an electrode, forming a ferroelectricmaterial comprising bismuth and at least one of hafnium oxide andzirconium oxide the electrode, and forming another electrode over theferroelectric material.

Referring to FIG. 2, a memory cell 200 including the capacitor 100 isshown. The memory cell 200 includes a substrate 210 and a source region214 and a drain region 212 formed within the substrate 210. Thesubstrate 210 may be a semiconductor substrate, a base semiconductormaterial on a supporting substrate, a metal electrode, or asemiconductor substrate having one or more materials, structures, orregions formed thereon. The substrate 210 may be a conventional siliconsubstrate or other bulk substrate including semiconductor material. Asused herein, the term “bulk substrate” means and includes not onlysilicon wafers, but also silicon-on-insulator (“SOI”) substrates, suchas silicon-on-sapphire (“SOS”) substrates or silicon-on-glass (“SOG”)substrates, epitaxial layers of silicon on a base semiconductorfoundation, or other semiconductor or optoelectronic materials, such assilicon-germanium (Si_(1-x)Ge_(x), where x is, for example, a molefraction between 0.2 and 0.8), germanium (Ge), gallium arsenide (GaAs),gallium nitride (GaN), or indium phosphide (InP), among others.Furthermore, when reference is made to a “substrate” in the followingdescription, previous process stages may have been utilized to formmaterial, regions, or junctions in the base semiconductor structure orfoundation.

The memory cell 200 may include an access transistor including a gateoxide material 216 and a gate electrode 218. The capacitor 100 may beconnected to the drain region 212 of the transistor via a conductivecontact (e.g., a conductive plug) 220. The conductive contact 220 mayoverlie the drain region 212 and may directly contact the bottomelectrode 102 of the capacitor 100. The conductive contact 220 mayinclude a conductive material, such as, for example, tungsten, titanium,aluminum, copper, polysilicon, or other suitable conductive material.

The gate oxide material 216 may include a suitable dielectric material.In some embodiments, the gate oxide material 216 includes silicondioxide, or a high-k dielectric material such as zirconium oxide,hafnium oxide, aluminum oxide (Al₂O₃), yttrium oxide (Y₂O₃), or otherhigh-k dielectrics known in the art. The source region 214 and the drainregion 212 may be located on opposing sides of the gate oxide material216.

The gate electrode 218 may include a conductive material, such as, forexample, titanium, tantalum, tungsten, ruthenium, nitrides thereof,polysilicon, or other suitable conductive gate electrode material.

Sidewall spacers 222 may be disposed on a side of the gate oxidematerial 216 and the gate electrode 218. The sidewall spacers 222 maycomprise a dielectric material, such as silicon dioxide or siliconnitride.

An access line 224 (e.g., a digit line, a bit line, etc.) may be coupledto the source region 214 and configured to apply a voltage to the sourceregion 214. The access line 224 may include a conductive material suchas, for example, tungsten, titanium, tantalum, palladium, platinum,silicides thereof, polysilicon, or other suitable conductive material.

Although the memory cell 200 has been described as comprising thecapacitor 100 including the ferroelectric material 104, the disclosureis not so limited. In other embodiments, the memory cell 200 maycomprise a field effect transistor (FeFET). In some such embodiments,the gate oxide material 216 may comprise the ferroelectric material 104.Stated another way, the gate oxide material 216 may include aferroelectric material comprising at least one of hafnium oxide andzirconium oxide doped with bismuth, as described above with reference tothe ferroelectric material 104. In some embodiments, the ferroelectricmaterial 104 may overlie and directly contact the substrate 210.

In some embodiments, the memory cell 200 may include a ferroelectricmaterial 104 at the gate oxide material 216 and the capacitor 100.

In other embodiments, the ferroelectric material 104 (FIG. 1) may beincorporated in a ferroelectric tunnel junction (FTJ) or anotherferroelectric device. In some such embodiments, the ferroelectricmaterial 104 may be disposed between two metal electrodes comprising,for example, tungsten, titanium, copper, platinum, silver, gold,polysilicon, other electrode materials, and combinations thereof. Theferroelectric material 104 may have a thickness between about 5 Å andabout 50 Å, such as between about 5 Å and about 10 Å, between about 10 Åand about 20 Å, between about 20 Å and about 30 Å, or between about 30 Åand about 50 Å.

Accordingly, in one embodiment, a memory cell comprises a capacitoroverlying a conductive material in contact with a source region or adrain region. The capacitor comprises a first electrode over asubstrate, a ferroelectric material comprising hafnium oxide, zirconiumoxide, or a combination thereof and bismuth over the first electrode,and a second electrode over the ferroelectric material.

With reference to FIG. 3, depicted is a processor-based system 300. Theprocessor-based system 300 may include various electronic devicesmanufactured in accordance with embodiments of the present disclosure.The processor-based system 300 may be any of a variety of types such asa computer, camera, pager, cellular phone, wireless device, display,chip set, set-top box, personal organizer, control circuit, or otherelectronic device. The processor-based system 300 may include one ormore processors 302, such as a microprocessor, to control the processingof system functions and requests in the processor-based system 300. Theprocessor 302 and other subcomponents of the processor-based system 300may include or be coupled to memory cells, memory arrays, andsemiconductor devices including the ferroelectric material comprising atleast one of hafnium oxide and zirconium oxide doped with bismuth inaccordance with embodiments of the present disclosure.

The processor-based system 300 may include a power supply 304 inoperable communication with the processor 302. For example, if theprocessor-based system 300 is a portable system, the power supply 304may include one or more of a fuel cell, a power scavenging device,permanent batteries, replaceable batteries, and rechargeable batteries.The power supply 304 may also include an AC adapter; therefore, theprocessor-based system 300 may be plugged into a wall outlet, forexample. The power supply 304 may also include a DC adapter such thatthe processor-based system 300 may be plugged into a vehicle cigarettelighter receptacle or a vehicle power port, for example.

Various other devices may be coupled to the processor 302 depending onthe functions that the processor-based system 300 performs. For example,a user interface 306 may be coupled to the processor 302. The userinterface 306 may include input devices such as buttons, switches, akeyboard, a light pen, a mouse, a digitizer and stylus, a touch screen,a voice recognition system, a microphone, or a combination thereof. Adisplay 308 may also be coupled to the processor 302. The display 308may include a liquid crystal display (LCD), a surface-conductionelectron-emitter display (SED), a cathode ray tube (CRT) display, adigital light processing (DLP) display, a plasma display, an organiclight-emitting diode (OLED) display, a light emitting diode (LED)display, a three-dimensional projection, an audio display, or acombination thereof. Furthermore, an RF sub-system/baseband processor310 may also be coupled to the processor 302. The RF sub-system/basebandprocessor 310 may include an antenna that is coupled to an RF receiverand to an RF transmitter (not shown). A communication port 312, or morethan one communication port 312, may also be coupled to the processor302. The communication port 312 may be adapted to be coupled to one ormore peripheral devices 314, such as a modem, a printer, a computer, ascanner, or a camera, or to a network, such as a local area network,remote area network, intranet, or the Internet, for example.

The processor 302 may control the processor-based system 300 byimplementing software programs stored in the memory. The softwareprograms may include an operating system, database software, draftingsoftware, word processing software, media editing software, or mediaplaying software, for example. The memory is operably coupled to theprocessor 302 to store and facilitate execution of various programs. Forexample, the processor 302 may be coupled to system memory 316, whichmay include one or more types of volatile memory, such as dynamic randomaccess memory (DRAM). The system memory 316 may further include othertypes of volatile memory, non-volatile memory, or a combination thereof.In some embodiments, the system memory 316 may include semiconductordevices, such as the semiconductor devices including memory cells andmemory arrays including the ferroelectric materials described above.

The processor 302 may also be coupled to non-volatile memory 318. Thenon-volatile memory 318 may include one or more of STT-MRAM, MRAM,read-only memory (ROM) such as an EPROM, resistive read-only memory(RROM), and Flash memory to be used in conjunction with the systemmemory 316. The size of the non-volatile memory 318 is typicallyselected to be just large enough to store any necessary operatingsystem, application programs, and fixed data. Additionally, thenon-volatile memory 318 may include a high capacity memory such as diskdrive memory, such as a hybrid-drive including resistive memory or othertypes of non-volatile solid-state memory, for example.

FIG. 4 is a system 400, which may also be characterized as asemiconductor device or incorporated in a semiconductor device includingFeRAM cells having a capacitor, according to embodiments of thedisclosure. The system 400 may include peripheral devices 412 inoperable communication with a FeRAM cell 414, a grouping of which may befabricated to form an array of memory cells in a grid pattern includinga number of rows and a number of columns, or in various otherarrangements, depending on the system requirements and fabricationtechnology. The FeRAM cell 414 may include a cell core including thecapacitor 100, an access transistor 403, a conductive material that mayfunction as a data/sense line 404 (e.g., a bit line), a conductivematerial that may function as an access line 405 (e.g., a word line),and a conductive material that may function as a source line 406. Theperipheral devices 412 of the system 400 may include read/writecircuitry 407, a bit line reference 408, and a sense amplifier 409. Thecapacitor 100 may be substantially the same as the capacitor describedabove with reference to FIG. 1.

In use and operation, when a FeRAM cell 414 is selected to beprogrammed, a programming voltage may be applied to the FeRAM cell 414to change a polarization state of the ferroelectric material of thecapacitor 100. When the programming voltage is removed, theferroelectric material may exhibit a polarization, as described abovewith reference to the ferroelectric material 104 in FIG. 1. In a readoperation of the FeRAM cell 414, a voltage is used to detect a state ofthe ferroelectric material 104.

To initiate programming of the FeRAM cell 414, the read/write circuitry407 may generate a read voltage to the data/sense line 404 and thesource line 406. The polarity of the voltage between the data/sense line404 and the source line 406 may determine the polarization direction ofthe ferroelectric material in the capacitor 100. The programmed logicstate of the FeRAM cell 414 may be a function of the direction ofpolarization of the ferroelectric material of the capacitor 100.

To read the FeRAM cell 414, the read/write circuitry 407 may generate aread voltage to the data/sense line 404 and the source line 406 throughthe capacitor 100 and the access transistor 403. The programmed state ofthe FeRAM cell 414 may be related to a direction of the polarization ofthe ferroelectric material in the capacitor 100.

Accordingly, in one embodiment, a semiconductor device comprises anarray of memory cells, each memory cell of the array of memory cellscomprising a capacitor coupled to a conductive material in contact witha source region or a drain region. The capacitor comprises a firstelectrode and a second electrode, and a ferroelectric materialcomprising hafnium oxide, zirconium oxide, or a combination thereof andbismuth between the first electrode and the second electrode.

Accordingly, in other embodiments, an electronic system comprises aprocessor, a memory array operably coupled to the processor, the memoryarray comprising memory cells, each memory cell of the array of memorycells comprising a capacitor operably coupled to a conductive materialin contact with a source region or a drain region. The capacitorcomprises a first electrode, a ferroelectric material comprising hafniumoxide, zirconium oxide, or a combination thereof and bismuth adjacentthe first electrode, and a second electrode adjacent the ferroelectricmaterial on an opposite side thereof from the first electrode. Theelectronic system further comprises a power supply in operablecommunication with the processor.

EXAMPLE

FIG. 5A is a graph comparing a hysteresis curve of a bismuth-dopedferroelectric material, according to embodiments of the disclosure,compared to a hysteresis curve of a conventional undoped ferroelectricmaterial. The ferroelectric material was substantially the same as theferroelectric material 104 described above with reference to FIG. 1. Theferroelectric material included hafnium oxide doped with bismuth andcomprised hafnium bismuth oxide. The conventional ferroelectric materialincluded undoped hafnium oxide having a crystalline phase such that itexhibited ferroelectric properties. The ferroelectric materials weredisposed between a pair of electrodes (e.g., a top electrode and abottom electrode). The ferroelectric material including the bismuthexhibited a hysteresis curve 502 having a greater remnant polarization(P_(r)) compared to a hysteresis curve 504 of the conventionalferroelectric material. The ferroelectric material including bismuthexhibited both a positive remnant polarization and a negative remnantpolarization having a greater magnitude than a respective positiveremnant polarization and a negative remnant polarization of theconventional ferroelectric material.

FIG. 5B is a graph of a signal strength vs. cycle number of a memorycell including the ferroelectric material including bismuth, accordingto embodiments of the disclosure, compared to a signal strength vs.cycle number of a conventional memory cell including the conventionalferroelectric material comprising hafnium dioxide. FIG. 5B illustratesthat the memory cell including the ferroelectric material includingbismuth exhibited an about twenty-five percent (25%) greater for the 2P, value of the conventional ferroelectric material.

FIG. 5C is a graph illustrating a crystal phase of the ferroelectricmaterial including the bismuth compared to the conventionalferroelectric material. The ferroelectric material including the bismuthexhibited a greater peak at an angle of about 30.5° compared to theconventional ferroelectric material, indicating a more crystalline filmwith more grains oriented in the orthorhombic phase. Accordingly, theferroelectric material comprising hafnium bismuth oxide exhibited agreater crystallinity than the conventional ferroelectric material.

While certain illustrative embodiments have been described in connectionwith the figures, those of ordinary skill in the art will recognize andappreciate that embodiments encompassed by the disclosure are notlimited to those embodiments explicitly shown and described herein.Rather, many additions, deletions, and modifications to the embodimentsdescribed herein may be made without departing from the scope ofembodiments encompassed by the disclosure, such as those hereinafterclaimed, including legal equivalents. In addition, features from onedisclosed embodiment may be combined with features of another disclosedembodiment while still being encompassed within the scope of thedisclosure.

1. A semiconductor structure, comprising: an electrode; anotherelectrode; and a ferroelectric material between the electrode and theanother electrode and comprising an oxide of at least one of hafnium andzirconium, the oxide doped with bismuth.
 2. The semiconductor structureof claim 1, wherein the ferroelectric material comprises hafnium bismuthoxide.
 3. The semiconductor structure of claim 1, wherein theferroelectric material comprises bismuth at between about 0.1 atomicpercent and about 10.0 atomic percent of the ferroelectric materialbased on non-oxygen atoms of the ferroelectric material.
 4. Thesemiconductor structure of claim 1, wherein the ferroelectric materialcomprises bismuth at between about 0.3 atomic percent and about 1.0atomic percent of the ferroelectric material based on non-oxygen atomsof the ferroelectric material.
 5. The semiconductor structure of claim1, wherein the ferroelectric material further comprises at least one ofmagnesium, yttrium, strontium, niobium, tantalum, lanthanum, gadolinium,vanadium, phosphorus, potassium, scandium, ruthenium, selenium, calcium,barium, aluminum, arsenic, indium, and silicon.
 6. The semiconductorstructure of claim 1, wherein the ferroelectric material furthercomprises magnesium.
 7. The semiconductor structure of claim 6, whereinthe ferroelectric material comprises between about 0.3 part and about10.0 parts of bismuth and magnesium for every about 100 parts of hafniumand zirconium.
 8. The semiconductor structure of claim 1, wherein theferroelectric material comprises a uniform concentration of bismuththroughout a thickness thereof.
 9. The semiconductor structure of claim1, wherein the ferroelectric material has an orthorhombic crystalstructure.
 10. The semiconductor structure of claim 1, wherein the oxideof at least one of hafnium and zirconium comprises hafnium zirconate(HfZrO₄), the hafnium zirconate doped with bismuth.
 11. Thesemiconductor structure of claim 1, wherein the ferroelectric materialcomprises zirconium bismuth oxide.
 12. The semiconductor structure ofclaim 1, wherein an atomic percent of bismuth in the ferroelectricmaterial exhibits a gradient.
 13. The semiconductor structure of claim1, wherein the ferroelectric material has a thickness between about 10 Åand about 200 Å.
 14. The semiconductor structure of claim 1, wherein theferroelectric material comprises hafnium zirconium bismuth oxide.
 15. Asemiconductor device, comprising: an array of memory cells, each memorycell of the array of memory cells comprising a capacitor coupled to aconductive material in contact with a source region or a drain region,the capacitor comprising: a first electrode and a second electrode; anda ferroelectric material comprising hafnium oxide, zirconium oxide, or acombination thereof and bismuth between the first electrode and thesecond electrode.
 16. The semiconductor device of claim 15, wherein thefirst electrode overlies a base material and further comprising aferroelectric material comprising hafnium oxide, zirconium oxide, or acombination thereof over the substrate, the ferroelectric material dopedwith bismuth over the base material.
 17. The semiconductor device ofclaim 16, further comprising a gate electrode overlying theferroelectric material over the base material.
 18. The semiconductordevice of claim 16, wherein the ferroelectric material comprises bismuthat between about 0.1 atomic percent and about 0.3 atomic percent of theferroelectric material based on non-oxygen atoms of the ferroelectricmaterial.
 19. The semiconductor device of claim 16, wherein theferroelectric material further comprises at least one of aluminum andmagnesium.
 20. A method of forming a semiconductor structure, the methodcomprising: forming an electrode; forming a ferroelectric materialcomprising bismuth and at least one of hafnium oxide and zirconium oxideover the electrode; and forming another electrode over the ferroelectricmaterial.
 21. The method of claim 20, wherein forming a ferroelectricmaterial comprises forming hafnium bismuth oxide.
 22. The method ofclaim 20, wherein forming a ferroelectric material comprises forming theferroelectric material to comprise between about 0.1 atomic percent andabout 10.0 atomic percent bismuth based on non-oxygen atoms of theferroelectric material.
 23. The method of claim 20, wherein forming aferroelectric material comprises forming the ferroelectric material toexhibit an orthorhombic crystal structure.
 24. An electronic system,comprising: a processor; a memory array operably coupled to theprocessor, the memory array comprising memory cells, each memory cell ofthe array of memory cells comprising a capacitor operably coupled to aconductive material in contact with a source region or a drain region,the capacitor comprising: a first electrode; a ferroelectric materialcomprising hafnium oxide, zirconium oxide, or a combination thereof andbismuth adjacent the first electrode; and a second electrode adjacentthe ferroelectric material on an opposite side thereof from the firstelectrode; and a power supply in operable communication with theprocessor.